The invention relates to communication networks in general. More particularly, the invention relates to a radio link protocol for increasing bandwidth efficiency for a network.
The demands on an individuals personal and professional time has created the need to communicate with others while on the move. Cellular systems provide this capability. As the number of individuals seeking to use cellular services increases, however, cellular systems are quickly running out of capacity. The term xe2x80x9ccapacityxe2x80x9d loosely refers to the number of cellular calls a system can carry at any one time. This is evidenced by the rising number of xe2x80x9cbusyxe2x80x9d signals the average cellular user receives while attempting to place a call in heavily populated areas such as within the downtown portion of a city. Consequently, cellular providers are turning towards digital cellular technologies to increase the capacity of their systems. Accordingly, this movement led to the establishment of a digital cellular standard in the United States referred to as Electronic Industries Association (EIA) Interim Standard IS-136, Rev 1.1, xe2x80x9c800 MHz TDMA Cellularxe2x80x94Radio Interfacexe2x80x94Mobile Stationxe2x80x94Base Station Compatabilityxe2x80x94Digital Control Channel,xe2x80x9d Oct. 11, 1995 (IS-136).
IS-136 defines a digital cellular system utilizing a variety of technologies to enhance the capacity of a system, such as using Time Division Multiple Access (TDMA), voice compression using Vector Sum Linear Prediction Coding (VSELP), and digital signaling. In addition to the above, IS-136 uses four-level phase shift keying (4-PSK) modulation. Modulation refers to the process of converting digital data into analog tones that can be transmitted over radio frequency (RF) spectrum.
A revision to IS-136 has been proposed. The revised IS-136 standard is referred to as xe2x80x9cIS-136+.xe2x80x9d IS-136+ attempts to achieve higher data rates over IS-136 by, among other things, increasing the modulation format from 4-PSK to 8-PSK or 16-Quadrature Amplitude Modulation (QAM). While increasing the modulation format increases the capacity of the system, it also increases the number of frame errors in the system, especially at low Signal-to-Noise Ratio (SNR).
Conventional IS-136 and IS-136+ systems use a radio link protocol referred to as EIA IS-130, Rev A, xe2x80x9c800 MHZ Cellular Systemsxe2x80x94TDMA Radio Interfacexe2x80x94Radio Link Protocol 1, xe2x80x9d Jul. 25, 1997 (IS-130) to correct frame errors. IS-130, however, is unsatisfactory for a number of reasons, two of which are discussed below.
The first problem with IS-130 is that it does not account for the SNR for a communication channel. IS-130 uses a technique referred to as xe2x80x9c⅚ encodingxe2x80x9d as a means of performing error correction for data transmitted from a transmitter to a receiver. The technique of ⅚ encoding means for every five bits of data, a sixth bit is introduced to correct errors. The problem with ⅚ encoding, however, is that it introduces a fixed amount of overhead for every five bits of actual data. If a communication channel has a high SNR, which means there is a lower likelihood of errors occurring during transmission, many times there is no need for the extra overhead. In other words, a block of transmitted data is received without any errors, and therefore the bandwidth spent transmitting the error correcting bits could have been used to transmit actual data. Conversely, if a communication channel has a low SNR, which means there is a greater likelihood of errors occurring during transmission, in many instances the errors are so numerous that ⅚ encoding cannot adequately correct them. Again, the resources used to transmit the error correcting bits are wasted. Moreover, this latter point also gives rise to a second problem associated with IS-130.
The second problem with IS-130 is that if the received block of data has errors that cannot be corrected, the entire block is discarded and is resent by the system. This means that the bandwidth spent transmitting and receiving the block is wasted. The time spent resending the block takes up resources that could otherwise be devoted to carrying extra calls for the system, i.e., increasing the capacity of the system.
In view of the foregoing, it can be appreciated that a substantial need exists for a radio link protocol that solves the above-discussed problems.
One embodiment of the invention includes a method and apparatus for sending blocks of data without any error correcting coding. If the block is received without an error then the next block of data is transmitted. If the block is received with an error, the receiving device sends a message requesting error correcting information. The transmitting device sends the error correcting information in specified increments until the receiving device can successfully decode the block without error. Once the block is received without errors, the next block of data is transmitted.
With these and other advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein.